1. Field of the Invention
The present disclosure generally relates to a sheet conveying apparatus and an image forming apparatus using the same, for example, printers, facsimiles, copiers, and multifunctional machines including functions of printer, facsimile, and copier.
2. Discussion of the Related Art
A conventional image forming apparatus may include an image bearer, an image fixing device, a transfer-sheet storage device, a transfer-sheet size detecting device, a conveyance device, a transfer-sheet detecting device, a timing device, an operational device, and a control device. The control device uses a first threshold and a second threshold smaller than the first threshold for every transfer-sheet size. The first threshold is used for detecting a sheet jam on the transfer-sheet conveyance path.
When the transfer-sheet conveyance time of a sheet, which is determined by the transfer-sheet detecting device and the timing device, is longer than the first threshold, a sheet jam is diagnosed and the image forming operation is stopped immediately. When the transfer-sheet conveyance time is shorter than the first threshold but not shorter than the second threshold and this situation is detected two consecutive times or more, the transfer-sheet size is considered irregular. In this case, conveyance of the following transfer sheet is prohibited, and an image forming operation is stopped after forming an image on the already fed transfer-sheet and discharging the sheet from the image forming apparatus. When the transfer-sheet conveyance time is shorter than the first threshold but not shorter than the second threshold and this situation is not detected consecutively, an image forming operation is allowed to continue.
In the image forming apparatus, the sheet length is measured using a sheet sensor disposed along the sheet conveyance path. The sheet length is compared with two or more thresholds, the number of which is determined based on the sheet size preset in the image forming apparatus, to detect a sheet jam and a sheet of irregular size. When the sheet length is different from the preset sheet size, the sheet is ejected without stopping the conveyance (i.e., without regarding the situation as a sheet jam). Therefore, at least one sheet must be conveyed to diagnose a sheet jam. When the sheet size is erroneously preset, one sheet and ejecting energy are consumed in vain.